I am not nearly a ceremonious enough person to hardly ever feel that I have the right to talk about other people's manners, except as a somewhat necessary part of raising my own daughters.
However, each year at some point, I observe a startling lack of beach etiquette on a point that simply must be addressed.
Do not feed the seagulls if you are near other people.
Seagulls are cool and it can be fun to feed them but you need to be courteous about the people around you. If a family is all set up with a tent and toys and having a great time near you, they do not want to be pooped on. You need to save your seagull feeding for when you are well away from other people who don't want to be pooped on.
That is all.